I don't know about the strattera, but I've been on and off Adderall for several years. I more or less self-medicate under my psychiatrist's supervision. sometimes I take my maximum allowed dosage and at others I stop taking it completely depending on my mental state at any given time. I've never had any problems when I stop taking it - and I take a pretty large dose usually.
The thing you'd have to be careful of would be stopping and starting. If I've been off it for a while, then need to start again, I can't start taking my full daily dosage right away. I have to build up to it again. Adderall is an amphetamine, after all.